Recent years, flexible displays are receiving quite a bit of attention. The demand for flexible displays that are foldable, bendable or rollable is being driven due to the customers' desire for larger portable displays. Further, the solution process and the roll-to-roll process, if available, can make it possible to produce such flexible displays at lower cost. At this point, the requirement is the use of a substrate as flexible as plastic or stainless steel, which requires the lower processing temperature of 300° C. or below. Many researches have recently been devoted to the organic thin film transistor (OTFT) as a transistor for driver circuit that can be produced at such a low temperature.
For the sake of high definition and low-power driving, an active matrix (AM) driving method is necessary. The inorganic transistor like silicone, currently available, is fabricated at high temperature and liable to breakage when bent or stretched, so there is a limit to apply the inorganic transistor to flexible and stretchable displays. Further, the solution process is impossible to use, resulting in the limitation to use in combination with another substances. Therefore, there are many researches in progress on the organic thin film transistors (OTFTs) that are easily fabricated at low temperature, available to the solution process and resistant to bending.
The organic thin film transistor, as a driving device for next-generation display, has been actively studied and expected to use in the fabrication of radio frequency identification (RFID) tags that are applicable to the recognition of individual item units. The organic thin film transistor, using an organic semiconductor film rather than a silicone film as a semiconductor layer, can be classified according to the material of the organic film into a low-molecular organic thin film transistor, such as an oligothiophene- or pentacene-based organic thin film transistor, and a high-molecular organic thin film transistor, such as a polythiophene-based organic thin film transistor.
On the other hand, a process for injecting a dopant is carried out on the semiconductor layer of the thin film transistor. The conventional methods related to the dopant injection process involve deposition of a dopant on an organic semiconductor thin film in a high-vacuum chamber by the vacuum-based thermal deposition technique or application of a dopant in the form of a solution on an organic semiconductor thin film by the spin coating process.
Many research organizations are making studies on the techniques for doping a semiconductor using a dopant for semiconductor, most of which techniques involve applying a dopant on an organic semiconductor thin film in a high-vacuum chamber by deposition or applying a dopant in the form of a solution on an organic semiconductor thin film by spin coating.
Accordingly, there is the difficult in the technical injection of different dopants when semiconductors of different properties are formed on the substrate.